Liquid injection molding inhibitors for curable compositions

ABSTRACT

Acetylenic maleates, fumarates and related derivative compounds are new compositions of matter having the formula: 
     
         R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2 
    
     wherein R 1  may be an organic moiety containing at least two carbon atoms triply bonded one to the other as: 
     
         --C.tbd.C-- 
    
     and R 2  may be hydrogen, an organic moiety, or R 1  ; suitable for use as liquid injection molding inhibitors either singly or in combination with themselves or other liquid injection molding inhibitors when used for the process of liquid injection molding curable compositions enabling an increase in the size of articles manufactured therefrom, which new compositions of matter cure into the polymerizable or curable resins thereby creating new compositions of matter as cured resins from which said articles of manufacture are produced.

This is a divisional of co-pending application Ser. No. 08/588,594 filedon Jan. 18, 1996, which is a divisional of Ser. No. 08/096,314 filed onJul. 23, 1993, now issued U.S. Pat. No. 5,506,289.

FIELD OF THE INVENTION

The present invention relates to translucent, high strength,organopolysiloxane, liquid injection molding compositions, liquidinjection molding inhibitors for use with curable compositions suitablefor liquid injection molding, and articles manufactured therefrom andtherewith using the techniques of liquid injection molding.

BACKGROUND OF THE INVENTION

Note: In the present specification, the word resin has been used withtwo meanings customary in the art. The first meaning refers to acomposition that is injected into a liquid injection molding apparatusand is very broad with respect to the chemical composition of itscomponent parts. The second meaning is more specific to the chemistry oforganopolysiloxanes and related silicone polymers, referring there toMQ, MDQ, MTQ, or MDTQ and similar compositions that may or may notcomprise a precursor feedstock to a liquid injection molding apparatus.

Liquid injection moldable organopolysiloxane compositions are known andused. A problem with all such compositions is that the hardness, tensilestrength, elongation and tear are so interdependent among themselves andalso with the viscosity of the uncured liquid precursor that it isdifficult to improve one property without deleterious effects on theother properties. Additionally, the kinetics and thermochemistry of theliquid injection molding process and the compositions used therewithhave been such that only small lightweight articles of manufacture couldbe made by the techniques of liquid injection molding because of thespeed with which the liquid precursor cures once it has been injectedinto the mold.

Liquid injection molding organopolysiloxane compositions are typicallyprovided as two components that are mixed immediately prior to use. Bothcomponents contain alkenyl polymers, fillers, and in some cases resins.The first component contains a platinum catalyst while the secondcomponent contains a hydride cross linker and cure inhibitors. The twocomponents are mixed immediately prior to use in the injection moldingapparatus. In addition to providing a so-called formulation pot-life,the inhibitor must prevent curing of the curable composition until themold is completely filled. Once the mold is completely filled theinhibitor must then allow for a rapid cure of the curable orpolymerizable composition in order to ensure a short cycle life.

U.S. Pat. Nos. 3,884,866 and 3,957,713 describe high strength additioncured compositions suitable for low pressure liquid injection molding.These compositions comprise a first component containing a highviscosity vinyl end-stopped organopolysiloxane, a low viscosity vinylcontaining organopolysiloxane, filler, and platinum catalyst which iscured by mixing with a second component containing a hydrogen siliconecomposition. This composition has a low durometer, ca 20-35 Shore A,and, moreover it is difficult to increase the durometer or hardnesswithout adversely affecting other properties.

U.S. Pat. No. 4,162,243 discloses compositions similar to the previouslyreferenced compositions but they contain as the most importantdistinction, fumed silica that has been treated withhexamethyldisilazane and tetramethyidivinyidisilazane. The compositionsof the '243 patent cure to elastomers having high hardness with goodretention of other properties including strength, elongation, and tearin addition to having a low viscosity in the uncured state.

U.S. Pat. No. 4,427,801 extends the teaching of the '243 patent byincorporating a MM^(Vi) Q resin in addition to the vinyl containingtreated fumed silica. This produces elastomers having even a higherhardness and tear strength but has the disadvantage of highercompression set and lower Bashore resilience.

It is an object of the present invention to produce a liquid injectionmolding organopolysiloxane composition having high hardness and tearstrengths without resultant adverse effects on other physicalproperties, such a composition being particularly suited to theinjection molding of large silicone rubber articles.

It is an additional object of the present invention to produce curableliquid injection molding compositions preferably organopolysiloxanecompositions that additionally have good shelf stability and good moldrelease, and may be employed in the manufacture of large silicone rubberarticles.

The manufacturing technique of liquid injection molding typically hasbeen liquid injection moldingited to small parts, usually materialsweighing less than from about 5 to about 50 grams. Advances intechnology are allowing liquid injection molded parts to become larger.Larger parts require larger molds. Larger molds require more time tofill the mold with resin and thus curing must be inhibited for longertimes in order to allow the mold to fill before cure may be initiated.

It is an additional object of the present invention to provide novelliquid injection molding inhibitors that will allow the manufacture oflarger articles of manufacture than heretofore were possible to be madefrom curable liquid organopolysiloxane compositions or other curableresins.

It is an additional object of the present invention to provide articlesof manufacture manufactured using curable liquid injection moldingresins containing the injection molding inhibitors of the presentinvention or mixtures comprising said injection molding inhibitorcompounds wherein said inhibitor compounds cure into the curable resinforming chemical bonds between the injection molding inhibitor compoundsof the present invention and the curable resin thereby forming anarticle of manufacture manufactured from a new composition of matter.

These and other objects will become apparent to those skilled in the artupon consideration of the present specification, examples, and claims.

DETAILED DESCRIPTION OF THE INVENTION

There is provided in the present invention a liquid injection moldingorganopolysiloxane composition, as a member of a class of moldable andcurable resins, combining low viscosity, high strength, good elongationwith exceptionally good hardness and tear strength which when combinedwith a new composition of matter useful as a liquid injection moldinginhibitor, which composition of matter is a compound useful forinhibiting premature curing in injection molding compositions having theformula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ may be any suitable organic moiety containing at least twocarbon atoms triply bonded one to the other as:

    --C.tbd.C--

and R₂ may be hydrogen, any suitable organic moiety, or R₁, saidcompound allowing larger articles of manufacture to be produced via thetechniques of liquid injection molding when the liquid consistsessentially of a curabie resin, particularly in the case of the presentinvention a organocolysiloxane. Such a low viscosity organopolysiloxanecomposition comprises:

(A) 100 parts by weight of an alkenyl, preferably vinyl containingpolyorganosiloxane component comprising:

(1) 70 to 98 parts by weight of a linear high viscosity alkenyl or vinylend-stopped organopolysiloxane having no more than 25 mole percent ofphenyl radicals and having a viscosity of from about 2,000 to about1,000,000 centipoise at 25° C.,

(2) 1 to 15 parts by weight of a linear low viscosity organopolysiloxanehaving at least one terminal alkenyl group per molecule, having analkenyl or vinyl content that may vary from 0.01 mole percent alkenyl orvinyl to 60 mole percent alkenyl or vinyl, having a viscosity thatvaries from 50 to about 5,000 centipoise at 25° C. and having no morethan 25 mole percent phenyl radicals, and,

(3) 1 to 15 parts by weight of an alkenyl or vinyl on chainorganopolysiloxane having from about 0.1 to about 25 mole percentalkenyl or vinyl, having a viscosity that varies from about 50 to100,000 centipoise at 25° C. and having no more than about 25 molepercent phenyl radicals;

(B) from about 5 to about 70 parts by weight of a filler;

(C) from about 0.1 to 50 parts per million of the totalorganopolysiloxane composition of a platinum catalyst;

(D) from about 0.1 to 10 parts by weight a SiH composition selected fromthe class consisting of hydrogen containing silanes and hydrogencontaining organopolysiloxane;

(E) optionally, from about 0.1 to about 6.0 parts by weight a hydroxycontaining organopolysiloxane fluid or resin having a viscosity rangingfrom about 5 to about 100 centipoise at 25° C.; and

(F) from about 0.001 to about 1.0 parts by weight per weight of thetotal liquid injection molding fluid of an injection molding inhibitorcompound or compounds, said injection molding inhibitor compound(s)selected from the group consisting of the mono- and di-alkynylsubstituted derivatives of maleic acid said compound or compounds havingthe formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ has the formula:

    --R.sub.3 --C.tbd.C--R.sub.4

wherein R₃ is selected from the group of divalent hydrocarbonradicalsconsisting of linear or branched alkyl radicals having from 1 to about10 carbon atoms, linear or branched alkenyl radicals having from 1 toabout 10 carbon atoms, linear or branched alkynyl radicals having from 1to about 10 carbon atoms, cycloalklyl radicals having from 3 to about 12carbon atoms, cycloalkenyl radicals having from about 3 to 12 carbonatoms, cycloalkynyl radicals having from about 8 to about 16 carbonatoms, fluorinated linear or branched alkyl radicals having from 1 toabout 10 carbon atoms, chlorinated linear or branched alkyl radicalshaving from 1 to about 10 carbon atoms, brominated linear or branchedalkyl radicals having from 1 to about 10 carbon atoms, fluorinatedlinear or branched alkenyl radicals having from 1 to about 10 carbonatoms, chlorinated linear or branched alkenyl radicals having from 1 toabout 10 carbon atoms, brominated linear or branched alkenyl radicalshaving from 1 to about 10 carbon atoms, fluorinated linear or branchedalkynyl radicals having from 1 to about 10 carbon atoms, chlorinatedlinear or branched alkynyl radicals having from 1 to about 10 carbonatoms, brominated linear or branched alkynyl radicals having from 1 toabout 10 carbon atoms, hydrocarbonoxy radicals containing at least twocarbon atoms, fluorinated hydrocarbonoxy radicals containing at leasttwo carbon atoms, chlorinated hydrocarbonoxy radicals containing atleast two carbon atoms, brominated hydrocarbonoxy radicals containing atleast two carbon atoms, aryl radicals, linear or branched alkyl arylradicals, fluorinated aryl radicals, chlorinated aryl radicals,brominated aryl radicals; fluorinated linear or branched alkyl-,alkenyl-, or alkynyl aryl radicals; chlorinated linear or branchedalkyl-, alkenyl-, or alkynyl aryl radicals; and brominated linear orbranched alkyl-, alkenyl-, or alkynyl aryl radicals; and wherein R4 isselected from the group of monovalent radicals consisting of hydrogen,linear or branched alkyl radicals having from 1 to about 10 carbonatoms, linear or branched alkenyl radicals having from 1 to about 10carbon atoms, linear or branched alkynyl radicals having from 1 to about10 carbon atoms, cycloalklyl radicals having from 3 to about 12 carbonatoms, cycloalkenyl radicals having from about 3 to 12 carbon atoms,cycloalkynyl radicals having from about 8 to about 16 carbon atoms,fluorinated linear or branched alkyl radicals having from 1 to about 10carbon atoms, chlorinated linear or branched alkyl radicals having from1 to about 10 carbon atoms, brominated linear or branched alkyl radicalshaving from 1 to about 10 carbon atoms, fluorinated linear or branchedalkenyl radicals having from 1 to about 10 carbon atoms, chlorinatedlinear or branched alkenyl radicals having from 1 to about 10 carbonatoms, brominated linear or branched alkenyl radicals having from 1 toabout 10 carbon atoms, fluorinated linear or branched alkynyl radicalshaving from 1 to about 10 carbon atoms, chlorinated linear or branchedalkynyl radicals having from 1 to about 10 carbon atoms, brominatedlinear or branched alkynyl radicals having from 1 to about 10 carbonatoms, hydrocarbonoxy radicals containing at least two carbon atoms,fluorinated hydrocarbonoxy radicals containing at least two carbonatoms, chlorinated hydrocarbonoxy radicals containing at least twocarbon atoms, brominated hydrocarbonoxy radicals containing at least twocarbon atoms aryl radicals, linear or branched alkyl aryl radicals,fluorinated aryl radicals, chlorinated aryl radicals, brominated arylradicals; fluorinated linear or branched alkyl-, alkenyl-, or alkynylaryl radicals; chlorinated linear or branched alkyl-, alkenyl-, oralkynyl aryl radicals; brominated linear or branched alkyl-, alkenyl-,or alkynyl aryl radicals; and triorganosilyl radicals and wherein R₂ maybe R₁ or selected from the group consisting of hydrogen, triorganosilylradicals, and siloxanes wherein the structural geometry of the compoundaround the double bond may be either cis or trans.

This composition may be either cured to an elastomer at room temperaturefor several hours or may be cured at elevated temperatures, such as, forexample, 200° C. for 10 seconds. In one embodiment, the abovecomposition is a two-component composition where the first component,contains at least all of ingredient (C), and the second component,contains all of ingredient (D) and the inhibitor compound(s) F.

The linear high viscosity alkenyl or vinyl end-stoppedorganopolysiloxane, A(1), has no more than 25 mole percent of phenylradicals and a viscosity of from about 2,000 to about 1,000,000centipoise 25° C., preferably from about 10,000 to about 500,000 at 25°C. These high viscosity organopolysiloxanes may be represented by thegeneral formula: ##STR1## where Vi stands for alkenyl or vinyl, R isselected from the group consisting of monovalent hydrocarbon radicalsand halogenated monovalent hydrocarbon radicals having up to about 20carbon atoms, and x may vary from about 100 to about 10,000 or evenhigher, preferably ranging from about 500 to about 2,000. Suitable highviscosity organopolysiloxanes are disclosed in U.S. Pat. No. 3,884,866hereby incorporated by reference.

The linear low viscosity organopolysiloxane, A(2), has at least oneterminal alkenyl or vinyl group per molecule, an alkenyl or vinylcontent that may vary from about 0.01 mole percent vinyl to about 60mole per cent vinyl, preferably from about 0.05 to about 10 mole percentalkenyl or vinyl, a viscosity that varies from about 50 to about 5,000centipoise at 25° C., preferably from about 50 to 1,000 centipoise at25° C.; and no more than about 25 mole percent phenyl radicals. Theselow viscosity organopolysiloxanes may be represented by the generalformula: ##STR2## wherein R' is selected from the group consisting ofmonovalent hydrocarbon radicals having up to about 20 carbon atoms,halogenated monovalent hydrocarbon radicals having up to about 20 carbonatoms, and alkenyl or vinyl, Vi is alkenyl or vinyl, and y may vary fromabout 1 to about 750. Suitable low viscosity organopolysiloxanes aredisclosed in U.S. Pat. No. 3,884,886 hereby incorporated by reference.

The alkenyl or vinyl on chain organopolysiloxanes, A(3), is important toobtaining the desired properties. Suitable alkenyl or vinyl on chainorganopolysiloxanes have from about 0.1 to about 25 mole percent alkenylor vinyl and preferably from about 0.2 to about 5 mole percent alkenylor vinyl, a viscosity that varies from about 50 to about 100,000centipoise at 25° C., preferably from about 100 to about 100,000centipoise at 25° C., and no more than about 25 mole percent phenylradicals. These organopolysiloxanes may be characterized as copolymersof (I) siloxane units having the formula:

    R.sub.a R.sub.b.sup.2 SiO.sub.(4-a-b/2)                    (3)

wherein R is selected from the group consisting of monovalenthydrocarbon radicals and halogenated monovalent hydrocarbon radicalshaving up to about 20 carbon atoms, R² is an olefinic hydrocarbonradical attached to silicon by a C--Si linkage, and generally containsfrom 1 to about 20 aliphatic carbons, either straight chain or branched,and preferably from 1 to about 12 carbon atoms linked by multiple bonds,with the stoichiometric subscript a ranging from a value of 0 to about 2inclusive, and the sum of the stoichiometric subscripts a and b rangesfrom about 0.8 to about 3.0 inclusive, and (II) organopolysiloxane unitshaving the structural formula:

    R.sub.c SiO.sub.(4-c)/2                                    (4)

wherein R is selected from the group consisting of monovalenthydrocarbon radicals and halogenated monovalent hydrocarbon radicalshaving up to about 20 carbon atoms, and the stoichiometric coefficient cranges in value from about 0.85 to about 2.5, inclusive. R² may be forexample, allyl, methallyl, butenyl, pentenyl, hexenyl, heptenyl,octenyl, ethenyl, and the like, but is preferably vinyl. The copolymerof (I) and (II) generally contains from about 0.5 to 99.5 mole percentof the compound of formula (3) above and from about 0.5 to 99.5 molepercent of the compound of formula (4) above. The preparation of thesecopolymers is well known in the art, as is taught in U.S. Pat. Nos.3,436,366 and 3,344,111 hereby incorporated by reference.

Preferred alkenyl or vinyl on chain organopolysiloxanes are linear andhave the general formula: ##STR3## wherein R is selected from the groupconsisting of monovalent hydrocarbon radicals and halogenated monovalenthydrocarbon radicals having up to about 20 carbon atoms, R² is anolefinic hydrocarbon radical attached to silicon by a C--Si linkage, andgenerally contains from 1 to about 20 aliphatic carbons, either straightchain or branched, and preferably from 1 to about 12 carbon atoms linkedby multiple bonds, and d and e are positive integers such that thepolymer contains up to approximately 20 mole percent R². Vi is alkenylor vinyl. Preferably R² is vinyl but may also be alkenyl, then thepolymer contains from 0.05 to 10 mole percent R², and the viscosityranges from about 300 to about 1000 at 25° C.

As previously recited, R is selected from the group consisting ofmonovalent hydrocarbon radicals and halogenated monovalent hydrocarbonradicals having up to about 20 carbon atoms, that is radicals normallyassociated as substituent groups for organopolysiloxanes. Thus theradical R may be selected from the class consisting of mononuclear andbinuclear aryl radicals such as phenyl, tolyl, xylyl, benzyl, naphthyl,alkylnaphthyl and the like; halogenated mononuclear and binuclear arylradicals such as chlorophenyl, chloronaphthyl and the like; mononucleararyl lower alkyl radicals having from 0 to 8 carbon atoms per alkylgroups such as benzyl, phenyl and the like; lower alkyl radicals havingfrom 1 to, 8 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl, octyl and the like either as straight or branched chainalkyl substituents, lower alkenyl radicals having from 2 to 8 carbonatoms such as vinyl, allyl, and 1-propenyl; halo lower alkyl radicalshaving from 1 to 8 carbon atoms such as chloropropyl, trifluoropropyl,and cycloalkyl radicals such as cyclobutyl, cyclopentyl and cyclohexyl.Though R may be any of the above, persons skilled in the art willreadily recognize that not every R can be a high molecular weightradical and that R should be chosen so as to not adversely affect thevinyl group reactions. Preferably R is a lower alkyl radical of 1 to 8carbon atoms, such as methyl, ethyl, and phenyl trifluoropropyl. Moreparticularly, R, is at least 70 percent by number methyl.

The SiH composition, (D), serves as a cross linking agent and may beselected from the class consisting of hydrogen containing silanes andhydrogen containing organopolysiloxanes. Hydrogen containingorganopolysiloxane can be characterized as copolymers containing atleast one unit per molecule having the formula:

    R.sub.f H.sub.g SiO.sub.(4-f-h)/2                          (6)

where the remaining siloxane units in the organopolysiloxane are withinthe scope of formula (4) above, with the notable exception that the R offormula (4) as well as the R herein should be saturated, f has a valueranging from 0 to about 2, inclusive; and the sum of f and g ranges fromabout 0.8 to about 3.0. The viscosity of the hydrogen containingorganopolysiloxane should range from about 5 to about 100 centipoise at25° C.

Included with the hydrogen containing organopolysiloxane described aboveare MQ resins having units of, for example, M(R)₂, SiO_(1/2) and SiO₂.Also included therein are MDQ, MTQ, MDT, and MTQ resins with hydrogensubstitution. Thus copolymer generally contains from 0.5 to 99.5 molepercent of the units of formula (6) and from 99.5 mole percent of theunits of formula (4).

The compounds, oligomers, resins or fluids designated MQ, MDQ, MTQ, MDT,and MT refer to the nomenclature explained in the research monograph byH. A. Liebhafsky, "Silicones Under the Monogram," published byWiley--Interscience division of John Wiley and Sons, New York(publication date 1978) at pages 99 and following. In the context of thepresent invention, substitutional isomerization such as M' beingdifferent from M but functioning as an "M" in terms of polymer buildingblocks as well as D' and D, T' and T, and Q' and Q, likewise; therebeing many varieties of each type of building block, are all encompassedby the simple shorthand notation referred to in the reference andherewith assume the same variability with respect to composition whileretaining their respective M, D, T, and Q functionality.

A preferred hydrogen containing organopolysiloxane is a linearorganopolysiloxane of the formula: ##STR4## wherein R is defined asabove, excluding unsaturated compounds, R³ is the same as R excludingunsaturated compounds and with the addition of hydrogen, h varies from 1to about 1000, and i varies from 5 to about 200. More preferably, hvaries from 10 to about 500 and i varies from 5 to about 200.

The hydrogen containing organopolysiloxane, (D), is utilized at aconcentration of anywhere from about 0.5 to 25 part by weight per 100parts by weight (A), and preferably at a concentration of from about 0.5to about 10 parts by weight per 100 parts by weight (A). It is desirablethat in the SiH material there is at least one hydrogen atom for everyvinyl group in (A) and preferably from about 1.1 to about 2.5 hydrogenatoms for every vinyl group.

Many types of platinum catalysts for this SiH olefin addition reactionare known and such platinum catalysts may be used for the reaction inthe present instance. When optical clarity is required the preferredplatinum catalysts are those platinum compound catalysts that aresoluble in the reaction mixture. The platinum compound can be selectedfrom those having the formula (PtCl₂ Olefin) and H(PtCl₃ Olefin) asdescribed in U.S. Pat. No. 3,159,601, hereby incorporated by reference.The olefin shown in the previous two formulas can be almost any type ofolefin but is preferably an alkenylene having from 2 to 8 carbon atoms,a cycloalkenylene have from 5 to 7 carbon atoms or styrene. Specificolefins utilizable in the above formulas are ethylene, propylene, thevarious isomers of butylene, octylene, cyclopentene, cyclohexene,cycloheptene, and the like.

A further platinum containing material usable in the compositions of thepresent invention is the cyclopropane complex of platinum chloridedescribed in U.S. Pat. No. 3,159,662 hereby incorporated by reference.

Further the platinum containing material can be a complex formed fromchloroplatininc acid with up to 2 moles per gram of platinum of a memberselected from the class consisting of alcohols, ethers, aldehydes andmixtures of the above as described in U.S. Pat. No. 3,220,972 herebyincorporated by reference.

The catalyst preferred for use with liquid injection moldingcompositions are described in U.S. Pat. Nos. 3,715,334; 3,775,452; and3,814,730 to Karstedt. Additional background concerning the art may befound at J. L. Spier, "Homogeneous Catalysis of Hydrosilation byTransition Metals, in Advances in Organometallic Chemistry, volume 17,pages 407 through 447, F. G. A. Stone and R. West editors, published bythe Academic Press (New York, 1979). Persons skilled in the art caneasily determine an effective amount of platinum catalyst. Generally, aneffective amount ranges from about 0.1 to 50 parts per million of thetotal organopolysiloxane composition.

One example utilized by current technology is the use of platinumcompounds that are complexed by highly coordinating ligands such as2,2'-bipyridyl. Pt bipyridyl exhibits good stability, i.e. there is nocuring at low temperatures, however, the curing at high temperatures,e.g. 350° F., is not as fast as might be desirable. Another approach isto premix the platinum and another inhibitor such as1-ethynyl-1-cyclohexanol. This mixture has a good low temperaturestability as well as a good cure rate at 350° F. but has a poor shelflife. When an inhibitor exhibits poor shelf life, the cure ratedecreases directly with increasing time of storage.

In order to obtain high tensile strength in the compositions of thepresent invention, it is desirable to incorporate a filler, (B), intothe composition. Examples of the many fillers that may be chosen aretitanium dioxide, lithopone, zinc oxide, zirconium silicate, silicaaerogel, iron oxide, diatomaceous earth, calcium carbonate, fumedsilica, silazane treated silica, precipitated silica, glass fibers,magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, alphaquartz, calcined clay, asbestos, carbon, graphite, cork, cotton,synthetic fibers, and the like.

The preferred fillers that should be utilized in the composition of thepresent invention are either a fumed silica or a precipitated silicathat has been surface treated. In one method of surface treatment, thefumed silica or precipitated silica is exposed to cyclicorganopolysiloxanes under heat and pressure. An additional method oftreating fillers is one in which the silica is exposed to siloxanes orsilanes in the presence of an amine compound.

A particularly preferred method of surface treating silica fillersemploys methyl silane silazane surface treating agents. Methylsilane orsilazane surface treated fumed or precipitated silica fillers exhibitthe property of flowing easily and also do not increase the lowviscosity of the uncured liquid precursor silicone composition. Aftercuring, silazane treated silicas impart an improved tear strength to thecured elastomer. Combining the silazane treatment with composition (A)for in situ treating seems to give the greatest improvement in physicalproperties. Silazanes treatments are disclosed in U.S. Pat. Nos.3,635,743 and 3,847,848 hereby incorporated by reference.

The filler, (B), is generally-utilized in a concentration of from about5 to about 70 parts, preferably 15 to 50 parts filler for each 100 partsby weight of (A). The preferred filler is silazane treated fumed silicaor mixtures of silazane treated fumed silica with silazane treatedprecipitated silica. This latter mixture is particularly preferredcontaining a weight ratio of fumed silica to precipitated silica ofabout 25/1 to about 1/1 and preferably from about 10/1 to about 5/1.

Hydroxy containing organopolysiioxane fluid, (E), may be added to extendthe shelf life of the liquid injection molding organopolysiloxanecomposition. Where silazane treated precipitated silica filler ispresent in the composition, the hydroxy containingorganopolysiloxane-fluid or resin may be added in conjunction with theprecipitated silica filler to obtain extended shelf life and moldrelease. Suitable hydroxy containing organopolysiloxane fluid has aviscosity of from about 5 to about 100 centipoise at 25° C. andpreferably from about 20 to 50 centipoise. These fluids may berepresented by the formula:

    R.sub.j (OH).sub.k SiO.sub.(4-j-k)/2                       (8)

where R is defined as above, j may range from 0 to about 3, preferably0.5 to about 2.0, k ranges from 0.005 to about 2, and the sum of j and kranges from about 0.8 to about 3.0. The hydroxy substitution on theorganopolysiloxane fluid or resin is primarily a terminal hydroxysubstitution.

To obtain mold release properties employing a combination of silazanetreated silica and composition (E), or to obtain extended shelf-lifeupon the addition of (E) alone, there should be present in composition(B) at least about 2 parts by weight silazane treated silica for each100 parts by weight of (A) and there should be present as composition(E) from about 1 to about 5 parts by weight for each 100 parts by weight(A).

The ingredients present in composition (C), component 1, may be packagedseparately from the ingredients present in composition (D),component II,until the time of cure. Compositions (A), (B), (E), and additives may bedivided between either component or wholly added to one component.Premature reactions are avoided in this manner during storage andtransport. When it is desired to form the cured silicone rubbercomposition, the two components are mixed into each other and thecomposition is allowed to cure. A fairly general practice is toformulate inhibitors such that the cure rates will allow storage of theresin within a liquid injection molding apparatus over short periods oftime such as a weekend without the curable composition curing duringstorage.

Traditionally liquid injection molding systems have two components, afirst component that contains a platinum containing catalyst, and asecond component that contains a hydride and an inhibitor. The twocomponents are mixed in a static mixer just prior to use in injectionmolding. Injection molding cavity temperatures are typically 300° F. ormore. The primary function of the liquid injection molding inhibitor isto prevent curing of the molding resin until the mold is filled andthereafter, the mold being filled, to allow a rapid cure to ensure shortcycle times. The two components may be injected molded directly ordissolved in solvents for application as a film or coating.

In injection molding, the mixing barrel and shot chamber must be cool inorder to prevent premature cure. The mold temperature generally variesfrom about 150° F. to about 500° F. Pigments, thixotropic agents,thermal stabilizers, and the like may be added according to theteachings in the art. It is particularly desirable to add inhibitors inorder to obtain a reasonable work life in the catalyzed material.Suitable inhibitors are taught in U.S. Pat. No. 4,256,870 herebyincorporated by reference. One of the most significant problems presentin the existing art is the liquid injection moldingitation on articlesize and weight imposed by the kinetics of the catalyzation and thethermochemistry of the injection molding process. These two parameterspresently interact to liquid injection moldingit the size of injectionmolded silicone rubber articles of manufacture.

U.S. Pat. No. 3,445,420, the teachings of which are hereby incorporatedby reference, discloses and claims curable compositions comprisingorganopolysiloxanes and acetylenic compounds having a boiling point ofat least 25° C. where the acetylenic compound has at least oneacetylenic moiety contained within the structural framework of themolecule. Although the use of the acetylenic compounds disclosed andclaimed in the '420 patent is well-known in the art, practice of theinvention represented by the '420 patent and related inventions has notenabled the liquid injection molding of larger molded articles ascontrasted with the present invention.

The manner in which the present invention improves upon the prior art isnot in the composition of the silicones or other resins used for liquidinjection molding but rather resides in the discovery of new compoundsthat function as inhibitors for the liquid injection molding of siliconefluids and other resins, these new compounds being the acetylenicmaleates and fumarates and related derivative novel maleate and fumaratecompounds that also function as liquid injection molding inhibitors. Themaleates and fumarates are derivative compounds of maleic and fumaricacids which are both four carbon unsaturated dibasic organic acids beingrelated one to the other as the cis and trans isomers of the same fourcarbon alkene chain, the (Z)but-2-ene-1,4-dioic orcis-but-2-ene-1,4-dioic acid being commonly known in the art as maleicacid and (E)but-2-ene-1,4-dioic or trans-but-2-ene-1,4-dioic acid beingcommonly known in the art as fumaric acid. Practitioners in the arttypically use the common names, i.e. maleic and fumaric acids ormaleates and fumarates as salts, esters, and other derivatives; theIUPAC names of the parent acids are specifically recited herein forpurposes of antecedence. The alkynyl maleates and fumarates comprisingthe compounds of the present invention may be half acid half ester orthe full ester and may contain more than one carbon carbon double bondand more than one carbon carbon triple bond. Having taught that thecompounds of the present invention comprise alkynyl maleates andfumarates and having taught the utility of those same compounds asliquid injection molding inhibitor compounds, the synthesis of analogouscompounds by those having ordinary skill in the art of such analogouscompounds containing either or both of higher levels of unsaturationwhether olefinic or acetylenic, i.e. alkenic or alkynic, and variousorganic substituents not specifically recited herein can generally beaccomplished and those analogous compounds would be expected on thebasis of the teachings herein and herewith published to have utility asliquid injection molding inhibitor compounds.

As a new composition of matter enabling the production of largerarticles of manufacture via the technique of liquid injection moldingusing curable silicone fluids or other curable resins, these newcompounds impart a novel and enhanced utility to all liquid injectionmolding compositions where they may be employed as well as to thearticles manufactured thereby and therewith. The present inventionrelieves the limitations of the prior art by enabling the manufacture ofinjection molded silicone rubber articles that weigh upwards of about100 g or more.

The novel inhibitor compounds of the present invention are cross-linkedor cured into the polymer molecules of the polymerizable or curableresin as a consequence of the process of liquid injection molding andcuring of the polymerizable or curable resin. Thus, the cured resins,containing as they do the cross-linked or cured derivative compounds ofthe new and novel inhibitor compounds of the present invention, aretherefor also new and novel compositions of matter. Thus, articlesmanufactured via liquid injection molding from cured resins containingthe cross-linked or cured new and novel inhibitor compounds of thepresent invention are themselves new and novel by reason of being madefrom a new and novel composition of matter. These new articles ofmanufacture may be made larger than heretofore possible by virtue of theimproved kinetic stabilization of the liquid injection molding resincompositions or mixtures thereof made possible by the properties of thenew and novel compounds of the present invention.

There are several additional embodiments to which the present inventionmay be directed. For example, mixtures of inhibitors that possessshorter inhibition times than the compounds of the present invention maybe formulated to contain the compounds of the present invention as wellthereby producing an inhibitor composition possessing an inhibition timeintermediate between the inhibition times of the particular componentinhibitor compounds. Thus the inhibition times of curable resin mixturesmay be more particularly controlled or adjusted depending on theproperties of the curable resins being used to produce articles ofmanufacture using the techniques of liquid injection molding, and theinstant technique.

EXAMPLES

The examples hereinafter presented serve to illustrate the utility ofthese new compositions of matter and instruct those skilled in the artconcerning the broad ranges of applicability and utility wherein suchnew compositions of matter may be employed. By presenting theseexamples, applicants do not intend to imply any liquid injectionmoldingitations on the extent of these new contributions to the art bythe mere presentation of an illustrative example.

Preparation of Inhibitor Compounds

The following inhibitors were prepared by combining the appropriateprecursor alcohol, maleic anhydride, toluene, and a catalytic amount ofmethane sulfonic acid (MSA) in a flask equipped with a "Dean Stark"trap, magnetic stirrer, and nitrogen atmosphere. The resulting reactionmixtures were heated to reflux until water was no longer observed to becollecting in the "Dean Stark" trap. At that point the reaction mixtureswere cooled to room temperature and treated with a solution of sodiumbicarbonate and then dried over anhydrous potassium bicarbonate. Thevolatile components were removed on a Buchi rotary evaporator and theesters then purified by distillation. The compounds were characterizedby NMR and gas chromotography. The following maleate esters wereprepared:

Example 1

Di(3-butynyl)maleate (DBTYNM). 24 g of 3-butyn-1-ol was reacted with 14g of maleic anhydride in 35 ml of toluene containing one drop of methanesulfonic acid as catalyst and 100 mg of hydroquinone as stabilizer.Subsequent experiments showed the hydroquinone to not be necessary.(bp=122-125° C./full vacuum, GC purity=97.4%) ¹ H NMR Data: (t, J=1.5Hz, alkynyl CH), 2.55 (dt, J=6, 1.5 Hz, CH₂ CC), 4.26 (t, J=6 Hz, CH₂--O), and 6.2 (s, maleate olefin CHs).

Di(3-butynyl)maleate (DBTYNM), second preparation, demonstratingreproducibility, 50 g of 3-butyn-1-ol was reacted with 31 g of maleicanhydride in 75 ml of toluene containing one drop of methane sulfonicacid as catalyst (bp=138-142° C./ca. 5 mm Hg) ¹ H NMR data: (t, J=1.5Hz, alkynyl CH), 2.55 (dt, J=1.5, 6 Hz, CH₂ CC), 4.26 (t, J=6 Hz, CH₂--O), and 6.2 (s, maleate olefin CHs).

Example 2

Dipropargyl maleate (DPM). This material was prepared via the reactionof 20 g of maleic anhydride with 46 g of propargyl alcohol in 325 ml oftoluene using 1 drop of methane sulfonic acid. Distillation of thematerial under vacuum gave 15.4 g of pure product (bp=125-130° C./ca.4-5 mm Hg, GC purity=98.6%). ¹ H NMR data: 2.58 (m, alkynyl CH), 4.8 (d,J=1.5 Hz, CH₂ --O), 6.35 (s, maleate olefin CHs).

Example 3

[presence of one drop of methanesulfonic acid. 11.5 g of DPTNM wasisolated from] Di(3-pentynyl) maleate (DPTNM). 15 g of 3-pentyn-1-ol wasreacted with 8.35 g of maleic anhydride in 25 ml of toluene and in thepresence of one drop of methanesulfonic acid. 11.5 g of DPTNM wasisolated from the reaction mixture (bp=134-140° C./full vacuum GCpurity=98.8%). ¹ H NMR data: 1.77 (t, J=3 Hz, CH₃), 2.52 (m, CH₂ CC),4.22 (t, J=7 Hz, CH₂ --O), 6.22 (s, maleate olefin CHs).

Example 4

Mono(3-butynyl)maleate (MBTYNM). The sodium bicarbonate layer from thesecond preparation of example 1 was carefully acidified withconcentrated HCl and then extracted with a mixture of toluene andacetonitrile. After drying over anhydrous sodium sulfate, the solventswere remove under vacuum to yield 8 g of crude mono(3-butynyl)maleate. ¹H (proton) NMR showed this material to contain approximately 6% DBTYNM,3% 3-butyn-1-ol, and 7% mono(3-butynyl)fumarate. ¹ H NMR data: 2.02 (t,J=2 Hz, alkynyl CH), 2.58 (dt, J=2, 7 Hz, CH₂ CC), 4.32 (t, J=7 Hz, CH₂--O), 6.36 (s, maleate olefin CHs), and 10.97(broad m, OH). The fumarateolefins were observed at 6.87 ppm, the diester DBTYNM maleate olefins at6.2, and the 3-butyn-1-ol CH₂ --O triplet could be observed at ca. 3.75ppm.

Example 5

Allyl 3-butynyl maleate (ABTNM). 5.0 g of MBTYNM (example 4) wascombined with 4.3 g allyl bromide, 30 ml terathydrofuran, 3.5 gpotassium carbonate, and 20 mg benzyltriethylammonium chloride. Theresulting reaction mixture was heated at reflux for 5.5 hours and thenallowed to cool to room temperature where it was stirred overnight. Themixture was then diluted with 50 ml of hexane and filtered to removesolids. The filtrate was washed with an additional 12 ml hexane and thenthe organics were combined and washed once with saturated sodiumbicarbonate solution and twice with water. After drying over anhydrouspotassium carbonate the solvents were removed under vacuum to yield 4.8g of product. NMR analysis showed that in addition to the maleate therewas some allyl 3 butynyl fumarate present as well(maleate:fumarate=9:1). ¹ H NMR data: 2.0 (t, J=2 Hz, alkynyl CH), 2.52(dt, J=2, 7 Hz, CH₂ CC), 4.28 (t, J=7 Hz, CC--CH₂ --O), 4.67 (d, J=8 Hz,allyl CH₂ --O), 5.2-6.2 (m, allylic olefin CHs), and 6.26 (s, maleateolefin CHs). The fumarate olefin peak was observed as a singlet at 6.84.

Example 6

Dipropargyl fumarate (DPF). This material was prepared in a differentmanner. For this example, 26 g of fumaryl chloride was reacted with 46 gof propargyl alcohol in 200 ml of dichloromethane, in the presence of37.8 triethyl amine and a small amount of dimethyl aminopyridine. Afterthe reaction was complete, the mixture was filtered and washed with 10%HCl to remove the amines. Concentration under reduced pressure yieldedthe product as a solid with a melting point of 78-80° C. (purified bysubliquid injection moldingation). ¹ H NMR data: 2.52 (t, J=1.5 Hz,alkynyl CH), 4.8 (d, J=1.5 Hz, CH₂ --O), 6.89 (s, fumarate olefin CHs).

Examples 7 through 19

Examples 7 through 18 consist of cure evaluation using the Monsantorheometer. Inhibitor cure performance was evaluated on a Monsanto MDR2000 rheometer. Such testing is conducted as follows: an uncured liquidinjection molding sample is placed in the sample chamber which ismaintained at the desired cure temperature. The clamps then close andthe top plate starts oscillating. As the material solidifies over time,the torque (S') increases until full cure is achieved. The mostimportant data obtained in these runs for the purposes of illustratingthe present invention are as follows:

1) the maximum S' value is related to the physical properties of thecured material;

2) integration of the torque curve allows the determination of curelevel vs. time; the times at 2% and 90% of reaction extent (T02and T90,respectively) are particularly significant as they provide informationas to when the cure reaction starts and finishes; and

3) the peak rate value can be used to evaluate the speed or velocity ofcure once it begins.

For a liquid injection molding composition to be useful in large partformulation and molding, there should be a significant and observabledifference in cure times at 250° F. and 350° F. Cure should be slow at250° F. to allow for mold filling and very fast at 350° F. in order toaccommodate short cycle times.

All of the Monsanto rheometer studies were conducted using a commonbase, formulation that was composed of the following weight fractions:

1) 65 parts of a 40,000 cps vinyl stopped polydimethylsiloxane polymer;

2) 25 parts of a 200 m² /g fumed silica;

3) 4 parts of a 450 cps dimethyl vinyl stopped fluid containingadditional vinyl on chain (1.6% vinyl);

4) 4 parts of a 500 cps trimethyl silyl dimethylvinylsilyl terminatedpolymer,

5) 1 part of a low molecular weight silanol polymer; and

6) 1 part of a silanol functional MQ resin.

Part "A" of the two part liquid injection molding material was preparedby combining 100 parts of the base formulation with 20 ppm Pt as aPt-divinyl tetramethylsiloxane complex. The part "B" materials wereprepared by combining 100 parts of the base formulation with theappropriate amount of inhibitor (see below in examples) and 3.2 parts ofa 3:1 blend of an M_(HQ) resin (ca. 1% H as SiH) and a trimethylsilylchain stopped dimethyl methyl hydrogen polysiloxane polymer (ca. 0.8% Has SiH). Complete liquid injection molding formulations were thenprepared by mixing "A" and "B" in a 1:1 weight ratio. In addition to theMonsanto rheometer runs, the test formulations were also cured incompression molded slabs (350° F., 15 minutes) so that physicalmeasurements could also be obtained on sheet materials preparedtherefrom. Tensile values were about 1190 psi, tear B values were about250 ppi, elongations were about 670%, 100% modulus was about 130 and thedurometer was about 39.

Included in Table I below are the Monsanto rheometer data fordi(3-butynyl)maleate (DBTYNM) based formulations as well as comparativedata on other known inhibitors such as diallyl maleate (DAM),1-ethynyl-1-cyclohexanol (ECH), 2,2'-bipyridyl, and2-methyl-3-butyn-2-ol (MB). The inhibitor amounts listed refer to theoverall concentration in the "A"/"B" blend. Concentrations of thevarious inhibitors in the base composition used for these comparativeevaluations have all been at a constant equimolar level.

                  TABLE I                                                         ______________________________________                                        Monsanto Rheometer Data for DBTYNM -vs- Controls                                                   Cure                                                       Example Inhibitor Temp. S' Max. T02 T90 Peak Rate                             Number (pph) (° F.) (lb.-in.) (sec.) (sec.) (lb.-in/min.)            ______________________________________                                         7a    DBTYNM    250     11.69 84   158  19.4                                    (0.1)                                                                         7b DBTYNM 350 11.24 6 17 97.0                                                 (0.1)                                                                         8a DBTYNM 250 12.7 152 257 15.3                                               (0.15)                                                                        8b DBTYNM 350 11.6 9 21 84.8                                                  (0.15)                                                                        9a DAM 250 10.67 60 117 24.1                                                  (0.2)                                                                         9b DAM 350 9.91 6 21 69.5                                                     (0.2)                                                                        10a DAM 250 11.25 90 234 14.8                                                  (0.3)                                                                        10b DAM 350 9.27 9 30 57.1                                                     (0.3)                                                                        11a 2,2'- 250 2.4 56 598 0.4                                                   Bipyridyl                                                                     (0.2)                                                                        11b 2,2'- 350 3.72 10 88 3.72                                                  Bipyridyl                                                                     (0.2)                                                                        12a ECH 250 10.42 8 18 85.3                                                    (0.08)                                                                       12b ECH 350 10.03 4 9 104.5                                                    (0.08)                                                                       13a MB 250 10.30 8 25 65.5                                                     (0.06)                                                                       13b MB 350 10.29 2 9 109.4                                                     (0.06)                                                                     ______________________________________                                    

As can be seen, DBTYNM provides a superior combination of slow cure at250° F. as well as a very rapid cure at 350° F. DAM provides areasonable differentiation between cure rates at the two temperatures,but does not match the results obtained with DBTYNM. Regarding the peakrates at 350° F. for these inhibitors, DBTYNM gave a much higher ratethan DAM. ECH and MB, while allowing for a rapid cure at 350° F., didnot provide an adequate inhibition at 250° F. Finally, 2,2'-bipyridylinhibited cure quite well at the lower test temperature but did notallow a rapid cure at the higher test temperature.

Included in Table II. are the Monsanto rheometer data obtained withother alkynyl maleates illustrative of the present invention:

                  TABLE II                                                        ______________________________________                                        Monsanto Rheometer Data for Other Alkynyl Esters                                                   Cure                                                       Example Inhibitor Temp. S' Max. T02 T90 Peak Rate                             Number (pph) (° F.) (lb.-in.) (sec.) (sec.) (lb.-in/min.)            ______________________________________                                        14a    DPF       250      9.89 16   76   53.9                                    (0.13)                                                                       14b DPF 350 10.67 4 14 97.6                                                    (0.13)                                                                       15a DPM 250 11.84 65 113 31.9                                                  (0.13)                                                                       15b DPM 350 11.27 6 16 98.3                                                    (0.13)                                                                       16a DPTNM 250 12.56 51 79 48.7                                                 (0.17)                                                                       16b DPTNM 350 10.07 5 16 86.1                                                  (0.17)                                                                       17a ABTNM 250 10.96 63 117 23.4                                                (0.14)                                                                       17b ABTNM 350 10.21 5 16 85.8                                                  (0.14)                                                                       18a MBTYNM 250 10.80 38 69 34.7                                                (0.1)                                                                        18b MBTYNM 350  9.52 5 15 85.5                                                 (0.1)                                                                      ______________________________________                                    

Listed in Table III. is the rheometer data for a formulation based on ablend of DAM and DBTYNM, an inhibitor of the present invention (1:1molar ratio). This blend was used at 0.14 pph overall concentration.

                  TABLE III                                                       ______________________________________                                        Monsanto Rheometer Data for a DAM/DBTYNM Blend                                                     Cure                                                       Example Inhibitor Temp. S' Max. T02 T90 Peak Rate                             Number (pph) (° F.) (lb.-in.) (sec.) (sec.) (lb.-in/min.)            ______________________________________                                        19a    DAM/      250     11.41 104  164  21.2                                    DBTYNM                                                                        (0.14)                                                                       19b DAM/ 350 10.57  8  21 77.5                                                 DBTYNM                                                                        (0.14)                                                                     ______________________________________                                    

This formulation is intermediate in behavior relative to the resultobtained with pure DAM or pure DBTYNM, as compared to data in Table I.

Examples 20 and 21

Liquid injection molding of parts. Two liquid injection moldingformulations with base compositions identical to those described in theMonsanto rheometer runs were prepared. Example 20 contained 0.075 pphDBTYNM and Example 21 contained 0.15 pph DAM. The target parts todemonstrate the advantages of the present invention were 75 g computerkeypads. The mold was heated to 380° F. and the liquid injection moldingcomposition was injected in 4 seconds and then allowed to cure for 10seconds for a total clamp time of 14 seconds. The DBTYNM containingformulation, Example 20, produced an excellent part by this procedure.The DAM based formulation was unable to completely fill the mold beforecuring began, because it cured prematurely, thus an incompletely formedpart was manufactured which was unacceptable.

Examples 22 through 25

FTIR Model studies. Some FTIR (Fourier Transform Infra-Red) modelstudies were conducted in order to show that the inhibitors of thepresent invention react into the liquid injection molding formulationsupon curing. The formulations used in these experiments were simplifiedin order to facilitate analysis. The formulations were composed of:

1) 10 parts of a 380 cps vinyl chain stopped fluid;

2) 0.04 parts inhibitor;

3) 0.24 parts of a 35 cps trimethylsilyl stopped methyl hydrogendimethylpolysiloxane polymer (ca. 1.1% H as SiH); and

4) 75 wppm Pt as a Pt-divinyl tetramethylsiloxane complex.

Thin films of the-low viscosity test formulations were spread on KBrsalt plates and then FTIR analysis was conducted using a Perkin-Elmer1600 series FTIR. The peak areas under the SiH peak (ca. 2160 cm⁻¹), asmall silicone standard peak (ca. 1950 cm⁻¹), and the maleate carbonylpeak (ca. 1730 cm⁻¹) were measured. The coated KBr salt plates were thenplaced in a Blue M forced air oven at 225-250° F. for various periods oftime. They were then cooled to room temperature and the infraredspectrum via FTIR was then redetermined in order to determine changes inthe SiH and carbonyl peaks. This process was repeated until the SiH peakceased to lose intensity at an appreciable rate, indicating that thecure reaction had become essentially complete.

Example 22

A formulation containing di-allyl maleate was tested first. Nearly 80%of the carbonyl absorbance disappeared before the SiH peak started todiminish. By the time the SiH peak had leveled off due to completion ofthe hydrosilation reaction, the carbonyl peak due to the inhibitor hadessentially disappeared.

Example 23

A formulation containing dibutyl maleate was also studied. Thisformulation behaved similarly to that in Example 22. The carbonyl peakcompletely vanished during cure.

Example 24

A formulation containing DBTYNM was studied. Significant carbonylabsorbance was observed even after the cure reaction had nearly gone tocompletion as evidenced by a leveling off of the disappearance of theSiH peak. This result indicates that even in a severe test where thematerial is spread out in a thin film and cured in uncovered in a forcedair oven that a large amount of the DBTYNM cures in. Therefore, in aliquid injection molding application where the material is sealed in amold, the DBTYNM inhibitor and related inhibitors would cure into thecured resin as well.

Example 25

The following formulation was evaluated by FTIR as described above:

1) 98 parts of a 225 cps vinyl chain stopped fluid was mixed with

2) 0.45 parts DPTNM;

3) 3 parts of a 35 cps trimethylsilyl stopped methyl hydrogen dimethylpolysiloxane polymer (ca. 1.1% H as SiH); and

4) 2 parts of a 0.5% Pt solution in a 450 cps dimethyl vinyl stoppedfluid containing additional vinyl on chain.

At the end of the reaction as judged by the leveling off of the SiHpeak, nearly 80% of the original carbonyl absorbance remained.Therefore, in a liquid injection molding application where the materialis sealed in a mold, the DPTNM inhibitor and related inhibitors wouldcure into the cured resin as well.

Having described the invention, that which is claimed is:
 1. A processfor controlling the period of time that a liquid injection molding resinor mixtures thereof is inhibited from curing comprising;(a) selectingone or more of the liquid injection molding inhibitor compounds havingthe formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected injection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereof.
 2. Aprocess for controlling the period of time that a liquid injectionmolding resin or mixtures thereof is inhibited from curingcomprising;(a) selecting one or more of the liquid injection moldinginhibitor compounds having the formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected injection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereofwherein saidselected inhibitor compound comprises dipropargyl maleate.
 3. A processfor controlling the period of time that a liquid injection molding resinor mixtures thereof is inhibited from curing comprising;(a) selectingone or more of the liquid injection molding inhibitor compounds havingthe formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected injection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereofwherein saidselected inhibitor compound comprises di(3-pentynyl)maleate.
 4. Aprocess for controlling the period of time that a liquid injectionmolding resin or mixtures thereof is inhibited from curingcomprising;(a) selecting one or more of the liquid injection moldinginhibitor compounds having the formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected injection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereofwherein saidselected inhibitor compound comprises mono(3-butynyl)maleate.
 5. Aprocess for controlling the period of time that a liquid injectionmolding resin or mixtures thereof is inhibited from curingcomprising;(a) selecting one or more of the liquid injection moldinginhibitor compounds having the formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected injection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereofwherein saidselected inhibitor compound comprises allyl 3-butynyl maleate.
 6. Aprocess for controlling the period of time that a liquid injectionmolding resin or mixtures thereof is inhibited from curingcomprising;(a) selecting one or more of the liquid injection moldinginhibitor compounds having the formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected injection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereofwherein saidselected inhibitor compound comprises dipropargyl fumarate.
 7. A processfor controlling the period of time that a liquid injection molding resinor mixtures thereof is inhibited from curing comprising;(a) selectingone or more of the liquid injection molding inhibitor compounds havingthe formula:

    R.sub.1 O.sub.2 C--CH═CH--CO.sub.2 R.sub.2

wherein R₁ is an organic moiety containing at least two carbon atomstriply bonded one to the other as:

    --C.tbd.C--

and R₂ is hydrogen, an organic moiety, or R₁ ; (b) contacting saidliquid injection molding inhibitor compound of part (a) with a secondliquid injection molding inhibitor compound or mixtures thereof having ashorter inhibition time than the selected inijection molding inhibitorcompound of part (a); and (c) contacting the mixture of liquid injectionmolding inhibitors comprising the inhibitor compounds of parts (a) and(b) with a liquid injection molding resin or mixture thereofwherein saidselected inhibitor compound comprises di(3-butynyl)maleate.